How to choose a consistent username

Consistency isn't a design preference. It's the difference between telling someone your name once and telling them five times.

Work the constraints in order

1. 15 characters — X's ceiling, and therefore yours.
2. Letters and numbers only — the intersection of what every platform allows.
3. No leading or trailing separators — several platforms quietly reject them.
4. Check the .com at the same time, because it's the one you can't get later.

Test the whole set at once

Checking platforms one at a time is how people end up with four out of five. Check them together, and treat a name as viable only if the whole set comes back clean.

Have a second name ready

The single best thing you can do is carry two candidates through the check instead of one. It turns "the name is taken" from a crisis into a decision.